A pack contains 18 pencil boxes. There are five pencils in each pencil box. Tiffany bought four such packs. How many pencils did Tiffany buy?

Number of packs bought by Tiffany = 4

Each pack contains 18 pencil boxes

∴ Number of pencil boxes bought by Tiffany = 4 × 18

Each pencil box contains 5 pencils

∴ Number of pencils bought = (4 × 18) × 5

= (4 × 5) × 18 .... (By commutative property)

= 20 × 18 = 360